heliair vs trimix

gallathan · 16th August 2007, 13:31

just thinking about blending heliar diluents vs blending trimix. Think blending trimix in dil cylinders at home may be error prone, so tempted to think about heliair, but have a dilema.

Seems you can go 2 routes, 1) Keep the PO2 of the heliair the same as my trimix dils i.e. 1.0. As heliair has a fixed N2 to O2 ratio (79.1:20.9) that results in high END's ~ 37/38M. I know the oxygen added by Rebreather to go from PO2 1.0 to PO2 1.3 will dilute the diluent a little, thus reducing the END, but not a lot.

2) Go with a dil with a PO2 of 0.836 instead of the 1.0 I normally use for Tx diluents. This is perhaps not the most optimal diluent for loop flushing, BUT does result in an end of 30M, like my timix bailouts, but concerned this will result in Rebreather having to add more O2 to the loop - reducing O2 duration and/or leading to more buoyancy issues.
Whats the normal practice for choosing a helair diluent, how do these factors get balanced?

**wedivebc** · 16th August 2007, 14:27

Quote: (Originally Posted by gallathan)

just thinking about blending heliar diluents vs blending trimix. Think blending trimix in dil cylinders at home may be error prone, so tempted to think about heliair, but have a dilema.

Seems you can go 2 routes, 1) Keep the PO2 of the heliair the same as my trimix dils i.e. 1.0. As heliair has a fixed N2 to O2 ratio (79.1:20.9) that results in high END's ~ 37/38M. I know the oxygen added by Rebreather to go from PO2 1.0 to PO2 1.3 will dilute the diluent a little, thus reducing the END, but not a lot.

2) Go with a dil with a PO2 of 0.836 instead of the 1.0 I normally use for Tx diluents. This is perhaps not the most optimal diluent for loop flushing, BUT does result in an end of 30M, like my timix bailouts, but concerned this will result in Rebreather having to add more O2 to the loop - reducing O2 duration and/or leading to more buoyancy issues.
Whats the normal practice for choosing a helair diluent, how do these factors get balanced?

I choose to use heliar because 1 it is easier to blend , 2 I don't own a helium analyzer so I can always predict my He based on my O2 content and 3 it gives me a mix that has a very acceptable END if you consider the planned O2 content I run is .2 below my setpoint so for 90m dive a 10/50 dil gives me an END of ~40m which is quite acceptable to me.

**nigelh** · 16th August 2007, 15:55

I don't like heliair but then I am a careful blender and I do have an analyser - would you dive a nitrox you hadn't personally measured on OC?

To get the nitrogen down to an acceptable level you end up going very hypoxic and that complicates the plan.

The recent 10m thread convinces me more and more that unnecessarily hypoxic bailouts and DIL are bad news.

**fireman** · 16th August 2007, 16:12

Hypoxic diluents are the devils playhouse. Your choice of Dil shouldn't be determined by convieniece, IMHO if you don't trust yourself and your system to blend say 18/50 or 21/50 when you need it, do you really trust yourself to be swimming around with hypoxic dil....
As a side note, my gas supplier sells 21/79 to hospitals, I was going to see if I could get that for a reasonable price, to have another tool in the quiver for gas blending.

lizardland · 16th August 2007, 16:48

Another vote for mixing for the depth. Less O2 to get up to setpoint on descent or if I have to flush, better dump rate and sphincter level if I have to SCR, I get the pO2 and END that I want when things are good, no unnecessary narc or hypoxic gas. I've dived for ten years on trimix with just the O2 analysed before helium meters were widely available so I'm fairly confident I can get the right mix when I do it myself. There was life before Rebreather's and helium analysers.

DepthCharge · 16th August 2007, 19:28

Quote: (Originally Posted by fireman)

As a side note, my gas supplier sells 21/79 to hospitals, I was going to see if I could get that for a reasonable price, to have another tool in the quiver for gas blending.

I know that it's rather expensive. Something in the neighborhood of $300.00+ USD per H cylinder. And that was 3-4 yrs ago.

JS1scuba · 16th August 2007, 20:10

If what you are saying is it is more difficult to mix small volumes of gas than it is to mix large volumes you are partially correct. Small volumes take more effort to keep the flow rate super slow and to keep the heat down.

A few tricks you can do are:

Use very good teqnique amd mix slowly. You will need three bottles, one of helium, one oxygen, and one air. Get them at the highest supply pressure possible.

or

Mix all your DIL in a twin-set to as high a pressure as possible then decant across to your dil cylinder. I'm using a set of TFX149s with 16/50 trimix in it we started at 270 bar and i think its down to 170 bar now and we have pulled 10 dill fills out of it. Once it hits 100 bar we will then decant and top the dill with air.

Another method of filling a nice dil is to mix with helium and a bottle of premix nitrox. Mix equal parts of helium and EAN 36 and you get 18/50 Mix helium and EAN 32 and you end up with 16% and so on.

A good mixing program will help you do this. You can also use unequal parts of EAN 36 and get some nice mixes as well. I have attached a chart I created for the NOAA Diving Manual Chapter 16 on Gas Mixing. The final column is oxygen/helium/nitrogen. Note NOAA runs OC PO2 at 1.4 and 1.6 atm. I should probably add a column for 1.3 as well but you get the point.

A note about analyzers. LONG before we had helium analyzers readily available we would be VERY careful with mixing and math and analyze with the O2 side only. If you are clever and careful you can use the PO2 meters in your rebreather to analyze your DIL as well. Just keep the O2 injector off. Or if you are that concerned about the mix get one of the TDL TekCheck Analyzers and you will always be spot on.

And now you wonder why they call it VooDoo Gas.

Cheers

Explorer · 16th August 2007, 20:48

Quote: (Originally Posted by gallathan)

just thinking about blending heliar diluents vs blending trimix. Think blending trimix in dil cylinders at home may be error prone, so tempted to think about heliair, but have a dilema.

Take an advanced gas blending course from your local dive shop. You will have the hands on practice you'll need.

**Dave Sutton** · 16th August 2007, 23:55

Quote: (Originally Posted by Explorer)

Take an advanced gas blending course from your local dive shop. You will have the hands on practice you'll need.

Assuming that the "certified mixing instructor" actually knows what he's doing, an all too rare event in my experience. Just make sure the quals are there. As Joel has said, mixing is as much art as science. It's more like cooking than chemisty.

Personally, I mix a little-o-this and a little-o-that and analize it and use it... The nice thing about Rebreather's is that it's not that critical.

Dave

sensor330 · 17th August 2007, 00:16

Quote: (Originally Posted by Dave Sutton)

Assuming that the "certified mixing instructor" actually knows what he's doing, an all too rare event in my experience. Just make sure the quals are there. As Joel has said, mixing is as much art as science. It's more like cooking than chemisty.

Personally, I mix a little-o-this and a little-o-that and analize it and use it... The nice thing about Rebreather's is that it's not that critical.

Dave

I have the same thoughts. Mixing gas isn't rocket science. I'm not a certified gas blender and I have no intention of paying any money for such a course.

Scott

16th August 2007, 13:31	#1 (permalink)
gallathan New Member Current Rebreather/s: Inspiration Vision Other Rebreather/s: Join Date: Mar 2006 Location: Laleham, Middlesex, England, UK Posts: 43	heliair vs trimix just thinking about blending heliar diluents vs blending trimix. Think blending trimix in dil cylinders at home may be error prone, so tempted to think about heliair, but have a dilema. Seems you can go 2 routes, 1) Keep the PO2 of the heliair the same as my trimix dils i.e. 1.0. As heliair has a fixed N2 to O2 ratio (79.1:20.9) that results in high END's ~ 37/38M. I know the oxygen added by Rebreather to go from PO2 1.0 to PO2 1.3 will dilute the diluent a little, thus reducing the END, but not a lot. 2) Go with a dil with a PO2 of 0.836 instead of the 1.0 I normally use for Tx diluents. This is perhaps not the most optimal diluent for loop flushing, BUT does result in an end of 30M, like my timix bailouts, but concerned this will result in Rebreather having to add more O2 to the loop - reducing O2 duration and/or leading to more buoyancy issues. Whats the normal practice for choosing a helair diluent, how do these factors get balanced?
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16th August 2007, 14:27	#2 (permalink)
wedivebc FIGJAM Current Rebreather/s: Megalodon Other CCR Other Rebreather/s: Not Bought Yet Inspiration Classic Sport Kiss Other CCR Join Date: Feb 2005 Location: Vancouver Island BC Canada Posts: 1,358	Re: heliair vs trimix Quote: (Originally Posted by gallathan) just thinking about blending heliar diluents vs blending trimix. Think blending trimix in dil cylinders at home may be error prone, so tempted to think about heliair, but have a dilema. Seems you can go 2 routes, 1) Keep the PO2 of the heliair the same as my trimix dils i.e. 1.0. As heliair has a fixed N2 to O2 ratio (79.1:20.9) that results in high END's ~ 37/38M. I know the oxygen added by Rebreather to go from PO2 1.0 to PO2 1.3 will dilute the diluent a little, thus reducing the END, but not a lot. 2) Go with a dil with a PO2 of 0.836 instead of the 1.0 I normally use for Tx diluents. This is perhaps not the most optimal diluent for loop flushing, BUT does result in an end of 30M, like my timix bailouts, but concerned this will result in Rebreather having to add more O2 to the loop - reducing O2 duration and/or leading to more buoyancy issues. Whats the normal practice for choosing a helair diluent, how do these factors get balanced? I choose to use heliar because 1 it is easier to blend , 2 I don't own a helium analyzer so I can always predict my He based on my O2 content and 3 it gives me a mix that has a very acceptable END if you consider the planned O2 content I run is .2 below my setpoint so for 90m dive a 10/50 dil gives me an END of ~40m which is quite acceptable to me. __________________ Cheers, Dave.... Man is the only animal burdened with the knowledge he will eventually die
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16th August 2007, 15:55	#3 (permalink)
nigelh New Member Current Rebreather/s: Inspiration Vision Other CCR Other Rebreather/s: Inspiration Classic Other CCR Join Date: Mar 2005 Location: Brighton, Sussex, UK Posts: 792	Re: heliair vs trimix I don't like heliair but then I am a careful blender and I do have an analyser - would you dive a nitrox you hadn't personally measured on OC? To get the nitrogen down to an acceptable level you end up going very hypoxic and that complicates the plan. The recent 10m thread convinces me more and more that unnecessarily hypoxic bailouts and DIL are bad news. __________________ nigelh
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16th August 2007, 16:12	#4 (permalink)
fireman rEvo combat swimmer Current Rebreather/s: rEvo Other CCR Other Rebreather/s: rEvo Other CCR Join Date: Nov 2006 Location: chicago Posts: 442	Re: heliair vs trimix Hypoxic diluents are the devils playhouse. Your choice of Dil shouldn't be determined by convieniece, IMHO if you don't trust yourself and your system to blend say 18/50 or 21/50 when you need it, do you really trust yourself to be swimming around with hypoxic dil.... As a side note, my gas supplier sells 21/79 to hospitals, I was going to see if I could get that for a reasonable price, to have another tool in the quiver for gas blending. __________________ Heres to you Capt. Bill Never Forget, and stay safe everyone.
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16th August 2007, 16:48	#5 (permalink)
lizardland Yak Current Rebreather/s: MK 15.X Home Build Other Rebreather/s: Classic Kiss Home Build Join Date: Mar 2005 Location: North... Posts: 1,186	Re: heliair vs trimix Another vote for mixing for the depth. Less O2 to get up to setpoint on descent or if I have to flush, better dump rate and sphincter level if I have to SCR, I get the pO2 and END that I want when things are good, no unnecessary narc or hypoxic gas. I've dived for ten years on trimix with just the O2 analysed before helium meters were widely available so I'm fairly confident I can get the right mix when I do it myself. There was life before Rebreather's and helium analysers. __________________ Can you imagine drifting along in the sea with your mouth open and a load of f***ing plankton going in? You'd like it, would you? www.westons-cider.co.uk Azerbaijani Association of Technical Divers Publicity Officer and Goat Wrangler
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16th August 2007, 19:28	#6 (permalink)
DepthCharge New Member Current Rebreather/s: Inspiration Classic Home Build Other Rebreather/s: Home Build Join Date: Mar 2005 Location: upstate NY Posts: 227	Re: heliair vs trimix Quote: (Originally Posted by fireman) As a side note, my gas supplier sells 21/79 to hospitals, I was going to see if I could get that for a reasonable price, to have another tool in the quiver for gas blending. I know that it's rather expensive. Something in the neighborhood of $300.00+ USD per H cylinder. And that was 3-4 yrs ago. __________________ Later, John It's better to beg forgiveness than ask permission
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16th August 2007, 20:48	#8 (permalink)
Explorer I will teach you a..... Current Rebreather/s: Evolution Megalodon Other Rebreather/s: Join Date: Sep 2005 Location: Alberta, Canada Posts: 754	Re: heliair vs trimix Quote: (Originally Posted by gallathan) just thinking about blending heliar diluents vs blending trimix. Think blending trimix in dil cylinders at home may be error prone, so tempted to think about heliair, but have a dilema. Take an advanced gas blending course from your local dive shop. You will have the hands on practice you'll need. __________________ TRAIN WRECKED.....
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16th August 2007, 23:55	#9 (permalink)
Dave Sutton Living on Animal Farm Current Rebreather/s: Sport Kiss MK 15.X rEvo Other CCR Azimuth Home Build Other Rebreather/s: Classic Kiss rEvo Other CCR Azimuth Home Build Join Date: Jun 2006 Location: Narragansett, Rhode Island and Hackettstown, New Jersey Posts: 2,511	Re: heliair vs trimix Quote: (Originally Posted by Explorer) Take an advanced gas blending course from your local dive shop. You will have the hands on practice you'll need. Assuming that the "certified mixing instructor" actually knows what he's doing, an all too rare event in my experience. Just make sure the quals are there. As Joel has said, mixing is as much art as science. It's more like cooking than chemisty. Personally, I mix a little-o-this and a little-o-that and analize it and use it... The nice thing about Rebreather's is that it's not that critical. Dave __________________ . "All animals are equal, but some animals are more equal than others" Professional Small Boy: Never Successfully Cubicled.
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17th August 2007, 00:16	#10 (permalink)
sensor330 Custom Title Allowed! Current Rebreather/s: Megalodon Other Rebreather/s: Not Bought Yet Inspiration Classic Join Date: Feb 2005 Location: Victoria, British Columbia, Canada Posts: 549	Re: heliair vs trimix Quote: (Originally Posted by Dave Sutton) Assuming that the "certified mixing instructor" actually knows what he's doing, an all too rare event in my experience. Just make sure the quals are there. As Joel has said, mixing is as much art as science. It's more like cooking than chemisty. Personally, I mix a little-o-this and a little-o-that and analize it and use it... The nice thing about Rebreather's is that it's not that critical. Dave I have the same thoughts. Mixing gas isn't rocket science. I'm not a certified gas blender and I have no intention of paying any money for such a course. Scott
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